In a move reminiscent of one done by Facebook in 2009, Twitter is close to completing an $800 million funding deal that will include a second part in which around $400 million of the total will be used to cash out current investors and also employees.

According to several sources close to the situation, the complex transaction could be completed within two weeks.

Along with basic funding needs, this is largely being done this way to give those with stakes in the San Francisco microblogging company an ability to monetize its privately held common stock and also to do this selling in a more organized--and legal--manner.

That is especially important since the company is not likely to go public for at least a year or more. And, while it could also be sold to a bigger company such as Google, that is also not in Twitter's immediate future.

Before this secondary follow-on, the first part of the deal will be a $400 million investment for preferred shares by new and also existing shareholders, as was reported by The New York Times last week.

That round will indeed value Twitter at $8 billion, as the Times reported, which is a higher number than in other earlier reports.

This is more than double what Twitter was valued at when it got $200 million in venture funding from Kleiner Perkins in December at a $3.7 billion valuation.

Once the latest investments are complete, Twitter's total cash haul since it was founded five years ago will be $760 million.

Key new moneybags are expected to be Russian investing heavyweight DST Global, which has invested in Facebook, Zynga and Groupon; as well as the digital growth fund of J.P. Morgan and perhaps others.

Current investors include Benchmark Capital, Union Square Ventures, Spark Capital and several other venture firms, as well as a spate of prominent angel investors.

The latest funding is an important one for Twitter and will up the pressure for its management, including CEO Dick Costolo, to really get its business growing in terms of revenue and profits.

Twitter is still struggling with coming up with a truly lucrative business model, and its execs have presented a number of them, such as promoted tweets, largely based on advertising.

It reportedly has $200 million in annual revenue from its efforts, which is still small in comparison to other Web 2.0 start-ups.

Interestingly, that was a similar situation to where Facebook found itself two years ago, when it allowed its employees to sell 20 percent of their shares.

That financing was part of a $100 million add-on to a $200 million investment in the social networking company by DST Global. At the time, the tender offer valued the company at $6.5 billion for the common stock, or $14.77 a share.

Of course, Facebook is worth upward of more than 10 times that now, so any Twitter sellers might want to consider their options carefully.

It is not clear exactly who can sell their Twitter shares, and in what amount, in the new deal. When Facebook did a similar move, for example, its top leadership could not sell any of their stakes.

A Twitter representative would not comment about any fund-raising.

But, interestingly, in an onstage interview at a Fortune magazine tech conference this week, Costolo criticized stock trading of the shares of popular start-ups on secondary exchanges as a "distraction." Like other companies, he said, Twitter had instituted stricter policies to limit the ability of its employees and investors to trade on those markets.